Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR sensor”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
FIG. 1 illustrates a cross-sectional view of an MR head 100, in accordance with the prior art. As shown, the MR read head 100 includes an MR sensor which is sandwiched between a hard bias layer HB which is in turn sandwiched between first and second shield layers S1 and S2. As is well known, the shield layers may incorporate gap layers G1 and G2 which provide insulation. The hard bias layer HB typically includes an upper layer 102 and a seed layer 104 therebeneath. One exemplary material commonly employed for the upper layer 102 is CoPtCr with the seed layer being constructed with Cr.
Lead layers L1 and L2 are sandwiched between the hard bias layer HB and shield layer G2 for providing a sense current to the MR sensor. Magnetic fields from a magnetic disk change the resistance of the sensor proportional to the strength of the fields. The change in resistance changes the potential across the MR sensor which is processed by channel circuitry as a readback signal.
The MR read head 100 is typically mounted to a slider which, in turn, is attached to a suspension and actuator of a magnetic disk drive. The slider and edges of the MR sensor and other layers of the MR read head 100 form an air bearing surface (ABS). When a magnetic disk is rotated by the drive, the slider and one or more heads are supported against the disk by a cushion of air (an “air bearing”) between the disk and the ABS. The air bearing is generated by the rotating disk. The MR read head 100 then reads magnetic flux signals from the rotating disk.
FIG. 2A illustrates a simplified cross-sectional view of the MR head 100 showing the hard bias layer HB and the MR sensor thereof. It should be noted that such simplified illustration is not drawn to scale, and includes crude blocks to simplistically show the overlap between the MR sensor and the hard bias layer HB, and the associated fields.
As shown FIG. 2A, the hard bias layer HB include positive poles 204 and negative poles 206. In use, the positive poles 204 and negative poles 206 of the hard bias layer HB produce first electromagnetic fields 208 in a first direction, and further produce a second electromagnetic field 210 in a second direction.
As shown in FIG. 2A, ends of the hard bias layer HB slightly overlap ends of the MR sensor. This is often the result of inherent defects in a photolithography process. This region of overlap defines a “domain wall” 212. Such domain wall 212 is typically where the first electromagnetic fields 208 of the hard bias layer HB are combated by the second electromagnetic field 210 of the MR sensor. FIG. 2B illustrates the MR sensor and the placement of the domain wall 212. As shown, the domain wall 212 is an area in which the first electromagnetic fields 208 are thwarted by the second electromagnetic field 210. Unfortunately, the overlap and resultant conflicting fields 214 in the MR sensor cause unfavorable noise during the use of the MR head.
One critical dimension of the MR head that affects the capability to read data recorded at high areal densities is the trackwidth TW. Note FIG. 1. The trackwidth TW of the MR read head is the length of the active or sensing region for the MR sensor. Unfortunately, the aforementioned overlap and resultant fields further cause a lack of trackwidth definition by blurring the sensing region.
There is thus a need for an MR head that does not suffer from such adverse noise and lack of trackwidth definition.
Still another characteristic associated with the MR head is the thickness of the hard bias layer HB. Often, such hard bias layer HB is designed to be as thick as possible in order to stabilize the MR sensor. Unfortunately, this increase in hard bias layer thickness results in a reduction in the thickness of the gap layers which are critical for preventing shorts involving the lead layers L1 and L2. This results in a greater occurrence of shorts.
There is thus a need for a MR head that is capable of adequately stabilizing the MR sensor without requiring a thick hard bias layer HB.